Enhancement mechanism of thermophysical properties of chloride salts by Al₂O₃/MgO nanoparticles with varying dispersion degrees and hybrid systems

Composite molten salts are widely used in concentrated solar power systems due to their excellent thermophysical properties. The dispersity of nanoparticles in molten salt has significant effect on heat transfer performance. This study uses molecular dynamics simulations to investigate the thermophysical properties of NaCl-KCl-MgCl₂ molten salts mixed with 10.0 wt% Al₂O₃ (CPCM_A), MgO (CPCM_M) or both Al₂O₃ and MgO (CPCM_AM) nanoparticles with varying dispersion degree. Results show the thermophysical properties of both CPCM_A and CPCM_M strengthen with increasing dispersion degree. The average thermal conductivity is improved by 7.2 % and 14.5 % respectively, while the specific heat is increased by 7.9 % and 7.6 % for CPCM_A and CPCM_M, respectively. However, as dispersion degree increases, the relative improvement degree in thermal conductivity and specific heat are different for CPCM_A and CPCM_M due to nanoparticle dispersion stability and variations in interfacial layer properties. In addition, comparing the thermophysical properties of CPCM_AM with CPCM_A and CPCM_M reveals that CPCM_AM nanoparticles are electrostatically attracted due to the opposite polarity of the surface charge, which drives the system from potential energy-dominated heat storage to kinetic energy-dominated dissipation mode, leading to a decrease in specific heat capacity. After that, the micro-interaction mechanism of nanoparticles and PCM, and its effect on thermophysical properties of CPCM are revealed by analyzing microscopic parameters such as diffusion coefficients, longitudinal number density, surrounding number density, surrounding charge density ratio, and potential energy. The present work provides critical theoretical support for understanding composite molten salt performance in high-temperature applications.